1. Field of the Invention
The field of the invention relates to ophthalmic equipment and procedures, such as, for example, equipment and procedures for performing cataract surgery.
2. Description of the Related Art
Certain ophthalmic procedures involve angular measurements of or on the eye. One ophthalmic procedure that generally involves angular measurements of the eye is a cataract surgery. Cataracts are clouded regions that can develop in the natural crystalline lens of an eye. A cataract can range in degree from slight clouding to complete opacity. Typically, formation of cataracts in human eyes is an age-related process. If left untreated, cataracts can lead to blindness. Surgeries have been developed for the treatment of cataracts. Typically, an incision is made in the eye and the natural crystalline lens is removed. An artificial lens called an intraocular lens (IOL) is then inserted in the capsular bag of the eye in place of the natural crystalline lens. The spherical optical refractive power of the IOL implant may be selected, for example, so as to place the eye in a substantially emmetropic state when combined with the refractive power of the cornea of the eye.
A cataract surgery typically requires a phaco incision, through which the patient's natural crystalline lens is removed and an artificial intraocular lens (IOL) is inserted, to be made at the limbus of a patient's eye. In some cases, it may be advantageous for this phaco incision to be made along a meridian at some specified angular orientation on the eye. Thus, the angular location of the phaco incision is measured in some way.
Cataract surgeries, and other ophthalmic procedures, may also involve additional angular measurements. For example, a cataract surgery may involve angular measurements so that the surgeon can align a toric IOL to a particular angular orientation. Toric IOL implants provide a degree of correction for any regular astigmatism which may exist in the patient's cornea. Such regular astigmatism results from a difference in the degree of curvature of the cornea in orthogonal meridians such that the eye has different focal lengths for light incident upon it in each of the planes of the two orthogonal meridians. Regular astigmatism has an axis associated with it that indicates its angular orientation.
A toric IOL implant has spherical and cylindrical refractive power. The cylindrical refractive power of the toric IOL more effectively corrects corneal astigmatism if it is accurately aligned with the angular orientation of the corneal astigmatism of the patient's eye. Therefore, there is a need for systems and methods capable of accurately determining the axis of cylindrical refractive power in the cornea to which the toric IOL implant should be aligned. In addition, there is a need for systems and methods that allow for more accurate positioning of the tonic IOL implant at the optimal angular orientation for correction of the astigmatic power of the cornea.
An ophthalmic surgery may also involve Limbal Relaxing Incisions (LRI) to be performed in an effort to correct corneal astigmatism. Even once the desired angular locations for these incisions have been determined, the surgeon still needs some means for actually identifying the desired angular locations on the eye. Other ophthalmic procedures may also involve certain angular measurements of the eye to be made.